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Abstract
During low temperature season, the growth and yield of leafy vegetables can decline due to low temperature and lack of sunlight. Cold stress can be alleviated and the growth and yield of crop can be improved by heating root-zone temperature. The recent increase in demand for aromatic leafy vegetables-including arugula (Eruca sativa L.), coriander (Coriandrum sativum L.), basil (Ocimum basilicum L.), and water spinach (Ipomoea aquatica Forsk.) – emphasized the need for year-round production. This study was conducted to investigate the effects of nutrient solution heating on root-zone temperature control, as well as its impact on shoot growth and yield. This experiment was conducted in a glass greenhouse located in Haman, Gyeongnam, Korea during low temperature season. Seedlings of four aromatic leafy vegetables were transplanted onto aeroponics bed and treatments were set for heating nutrient solution at three different temperatures －20°C(NSH20), 25°C(NSH25), 30°C(NSH30). The nutrition solution followed PBG composition for leaf vegetables and was continuously recirculated without discharge. Ionic concentrations and properties of the nutrient solution were investigated every three days, and growth and harvest measurements were taken at two and four weeks after transplanting. During the cultivation period, mean of minimum, mean, and maximum temperature per day inside the greenhouse were 13.75°C, 18.66°C, and 30.08°C, respectively. The lowest temperature was recorded at 9.97°C. In the control, the mean of root-zone temperature was 17.17°C and the lowest of root-zone temperature was 13.35°C, which could potentially prevent root development and reduce shoot growth due to cold stress. The average root-zone temperatures were 24.61°C in NSH30, 21.41°C in NSH25, and 18.62°C in NSH20. No significant differences in growth and yield were observed in cool-season grown vegetables, arugula and coriander, across the four different root-zone temperatures. In contrast, for warm-season grown vegetables, basil and water spinach, showed improved growth and yield with increasing root-zone temperature. Basil showed similar improvements at 25°C and 30°C, indicating that 25°C is sufficient and more energy-efficient. Water spinach showed a 107% yield increase in NSH30 compared to the control, and a 60% increase compared to NSH25, suggesting that maintaining a higher root-zone temperature is more suitable for maximizing its productivity. These findings demonstrate the importance of crop-specific root-zone temperature management in aeroponics during low temperature seasons.